It's interesting to note that the RN equipped Ark Royal and Eagle with F-4s versus the US Oriskany class. If I understand from checking the specs the deck of the Oriskany (and possibly the others) was stressed to handle aircraft as heavy as Phantom but were not fitted with the catapults and blast deflectors to handle them.
A friend of mine served as an Aviation Maitenance Officer onboard the Oriskany before and during Vietnam, and he said that's exactly why the F-4s were never carried about the Oriskany and her sisters, inadequate catapults and blast deflectors. Apparently the Navy didn't feel the ships could carry a large enough number of Phantoms for an adequate size airwing, so they didn't equip them to carry the aircraft. Personally, I think it was a political move so the Navy could justify asking Congress for funding to build larger supercarriers.